I have a salt water pool with an aquq-rite automatic electronic chlorinator. In summer I always have to add salt and cyanuric acid to keep things in balance, but now that it has turend colder (pool temp donw to 66 deg F) I am having trouble with all of the above. HTH 6-way pool tester indicates that hardness is good at 200-400ppm, but FC is at low end (oppm comparator), pH is reading yellow (below the loswest orange comparator - 6.4), total alkalinity is reading yellow (below the lowest green-yellow comparator - 0ppm) and cyanuric acid level is reading yellow (below the lowest orange comparotr - 0ppm), even though I've added two gallons of HCL in the past two days. My pool is around 35000 gal. Any suggestions?

Adding Muriatic Acid (31.45% Hydrochloric Acid or HCl) will lower the pH and TA. Your pH and TA are now way too low -- if they were low before you added the HCl, you should not have added that. 2 gallons is a lot of acid to add anyway. Even starting with a TA of 100 and a pH of 7.5, 2 gallons of acid in your 35,000 gallon pool would result in a pH of 6.7 and a TA of 71. I certainly hope your TA measurement is wrong since the normal TA test will only show 0 TA when the pH is at 4.5, but that's for the drop-based test while you are using test strips.

Right now, your pool is very corrosive and you immediately need to get the pH and TA up right away. I suggest adding pH Up or the equivalent which is Arm & Hammer Super Washing Soda (careful: not the laundry detergent). I would add at least 19 pounds (about 33 cups) of pH Up / Washing Soda or alternatively add a little more than twice that weight, 39 pounds of 20 Mule Team Borax which would be 8-1/3 boxes. The Borax will raise the pH without raising the TA as much. This should get you to around a pH of 7.0 at which point you can retest and adjust more from there.

You should really get a good test kit, the Taylor K-2006 from Taylor here or from Leslie's here or from poolcenter.com here or the even better TF100 test kit from tftestkits.com here. These kits are much more accurate than the test strips. The TF100 is more economical than the Taylor kit as it provides around 36% more tests due to larger reagent bottle sizes.

Thanks for the recommendation. It's really strange - the pool normally has run weak on chlorine genereation, and I always have to add CYA or HCL to get the pH and TA balance right per the test strips. I got new test strips and all fo a sudden everything looks off. I'll try to get a decent test kit tomorrow and re-test. Thanks,

With saltwater pools, having the pH rise is common so adding acid to lower the pH is typical, but having to add CYA is unusual since the CYA should not be going away. Cyanuric Acid (CYA), like Calcium Hardness (CH), only gets lowered through splash-out and backwashing.

As for the typical rise in pH, this occurs due to the production of hydrogen gas bubbles in the saltwater chlorine generator (SWG) that aerates the water driving out carbon dioxide. If you lower the TA level, you lessen this effect. If you add 30-50 ppm Borates to the pool, then that can also lower the effect by being an algaecide that lowers chlorine usage and lets you turn down the SWG.

Also, as the water gets colder in the winter and you are able to turn down your SWG output since the chlorine lasts longer in colder water, the rate of pH rise will slow down and you won't need to add as much acid.